Yes, the Part B penalty is 10% per 12 month period but the computations all depends on when the count starts and I do believe that it can be increments of months in a 12 month period too.
When 1st eligible for Part B and when there is no other credible coverage in place, you have an INITIAL ENROLLMENT PERIOD (IEP) - this is (3) months BEFORE your 65th birthday and it continues to (3) months AFTER your 65th birthday.
The penalty month count does not even start until the end of that IEP, meaning (3) months after a person turns 65.
To further complicate the matter, if a person misses this IEP and has no other appropriate coverage in place, there is ONLY a specific time period that the person can then sign up for Part B. January 1 - March 31 of the following year; this is the General Enrollment Period (GEP). Even if a person signs up during this GEP, their actual coverage does not begin until the following July.
SSA.gov - Medicare Part B Sign Up
from the link ~
In most cases, if you don’t enroll in Part B now [during the IEP], you will have to pay a late enrollment penalty for as long as you have Part B. You will have to wait until the next General Enrollment Period (from January 1 through March 31) to enroll in Part B and coverage will begin July 1 of that year. The penalty increases the longer you go without Part B coverage.
. . . . Can I enroll later?If you don’t sign up for Medicare Part B now [during the IEP], you may have to wait until the next General Enrollment Period, (January 1 through March 31 of each year) to sign up. Your coverage will start July 1 of that year and you’ll have to pay a late enrollment penalty. The penalty increases the longer you go without Part B coverage and you will pay 10% more for each 12-month period you could have had Part B but didn’t take it.
Here’s an example:
If you waited 2 full years (24 months) to sign up for Part B and didn’t have other coverage, you’ll have to pay a 20% late enrollment penalty (10% for each full 12-month period that you could have been enrolled), plus your standard Part B monthly premium ($134.00 in 2017).
$134.00 (2017 Part B standard premium)+ $26.80(10% [of $134.00] for each full 12-month period you could have had Part B) $160.80will be your Part B monthly premium for 2017. This amount is rounded to the nearest $.10 and includes the late enrollment penalty.
Note: The example above applies if you delayed enrolling in Part B for 24 months. You don’t pay a late enrollment penalty if you enroll before the first full 12-month period has passed or if you qualify for a Special Enrollment Period.
You’ll have to pay this late enrollment penalty as long as you have Part B
Just hitting that even 12-month penalty period would be hard - but that is gonna depend on your birthday date + (3) months after + how long to Jan.1 - March 31 + to July when the coverage starts.
It is my understanding that even though it says the penalty is 10% for a 12 month period, I believe that it is prorated by number of months that a person was without Part B coverage (and no other coverage that worked).
The reason that it increases is that the Part B premiums go up on an annual basis over time - unless restricted by the SS/Medicare law (hold-harmless provision).
It's Always Something . . . . Roseanna Roseannadanna